With the rapid development of the wireless communication technology, people's demand for the communication through the user equipments (UEs) (e.g., smart phones, tablet computers or the like) also increase. To satisfy the requirements of the users, new generations of mobile communication systems are being developed continuously, e.g., Long Term Evolution (LTE) communication systems, Worldwide Interoperability for Microwave Access (WiMAX) communication systems or the like.
When a user equipment (UE) is powered on, suffers a network disconnection or fails to synchronize with a base station in these mobile communication systems, a random access procedure may be initiated by the UE to obtain radio resources for subsequent data transmission with the base station. In the random access procedure, the UE transmits a random access request message on a particular channel broadcasted by the base station. The UE randomly selects one of a plurality of preambles defined by the communication system to generate a random access request message based on the selected preamble.
However, in addition to the common UEs, more and more kinds of wireless devices capable of mobile communication have been produced in recent years, e.g., Internet of Things (IoT) devices, Machine Type Communication (MTC) wireless devices or the like. When a large number of wireless devices (i.e., UEs, IoT devices, MTC devices and various kinds of wireless devices capable of mobile communication) initiate the random access procedure at the same time, each of these wireless devices selects a preamble randomly from the plurality of preambles of the same set. Therefore, it is likely that a same preamble is selected by multiple wireless devices at the same time to cause preamble collision between random access request messages transmitted by the wireless devices.
As the probability of preamble collision increases with the number of the wireless devices, the wireless device will re-select a preamble randomly to transmit a random access request message once the preamble collision occurs in the random access procedure. The operations of re-selecting a preamble randomly and transmitting the random access request message prolongs the time required for successfully accomplishing the random access procedure, and the wireless device even stops the random access procedure when the number of retransmission of the random access request message reaches an upper limit of the system. This causes failure of the data transmission between the wireless device and the base station, and moreover, leads to idleness of some radio resources of the base station.
Further, different wireless devices have different needs for data transmission. For example, UEs usually need real-time data transmission, while some IoT devices and MTC devices do not need real-time data transmission. Therefore, serious preamble collision may cause failure of the UEs to obtain resources for real-time data transmission, which results in a poor experience of the user.
Accordingly, an urgent need exists in the art to provide a random access mechanism that, despite of the increasing number of wireless devices, improves the probability of successfully executing the random access procedure by the wireless devices and especially UEs that need real-time data transmission so as to avoid idleness of the radio resources of the base station.